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sea91ray
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I have a 1995 previa. when I start the engine (in park) it jumps to very high rpms.

when i'm on the highway without touching the gas pedal it will go 90 mph. I have to fight the engine with the brake pedal to slow it down. what's up?

tk

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It's an over-run problem of some kind. Something is forcing the engine to keep running/accelerating when it shouldn't.

Depends on the engine type as to what the problem could be. If it's a diesel then it's a good bet that you've got injectors allowing fuel to flow into the bores or Oil is getting into the combustion chamber somehow.

If it's a petrol engine then my guess would be a sticking throttlebody or something in the throttle linkage.

Sorry, not definative answers but can't go any further without more details

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Sounds to me like the automatic choke is playing up.

If the choke came on when going down the motorway then your revs would go up meaning you would accelerate - which sounds like the problem you are having.

Anyway - best to get it checked out at your local garage

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Or perhaps the throttle position sensor.

Thats what I would say.... a mate of mine has the same problem on his ford focus... sounds very similar...

Either needs a clean or replacing.. shouldnt be too much/difficult tho apparently

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Or perhaps the throttle position sensor.

Thats what I would say.... a mate of mine has the same problem on his ford focus... sounds very similar...

Either needs a clean or replacing.. shouldnt be too much/difficult tho apparently

The TPS, fast idle control, or choke wouldn't cause it to accelerate up to 90 and need brakes to hold it back though.

Is it petrol or diesel?

If you have cruise control, it could have developed a fault. Otherwise it can only be a sticking throttle on a petrol engine.

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My mr2 does this but only when i start it up after not having used it all day or first thing in the morning - i thought this was just cold start though - so that the engine warmed up before you set off, it doesnt do it any other time :unsure:

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Nah, I'm with Mikeb on this one.

TPS, ISCV or Choke would only cause it to over run by a small amount and then only under no load. TPS would cause a ritch/lean mixture that might affect speed slightly, ISCV doesn't have enough volume throughput to do that and choke would again really only richen the mixture. Not push you up to 90Mph without touching the throttle

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My mr2 does this but only when i start it up after not having used it all day or first thing in the morning - i thought this was just cold start though - so that the engine warmed up before you set off, it doesnt do it any other time  :unsure:

Tegan, It's normal for MR2's and some other Toyotas to rev high at first start up. The MKI engine has a couple of sensors that work together on cold start - the TPS (throttle posision sensor), the Wax Stat, the water temp sensor and the air temp sensor. All these work together with the ECU until a predetermined running temperature is reached whilst doing this the revs will slowly drop to normal running range (around 800 - 1000rpm). Many poeple do a manual choke conversion (bypassing the wax stat) which allows them to run the car in summer without the need for high revs as it's not always needed and consumes fuel. And then in winter use the choke for as long as the engine needs it.

With normally asperated (no forced induction) engines it's not too good to leave the engine idling to running temp. You can pull away a few seconds after starting, but not rev higher than 3.5k before changing gear until you're certain Oil temp is right up.

The temp gauge on most dashboards relates to water temp not Oil temp. Oil takes a little longer to reach temp.

With Turbo'd engines it is advisable a low running temp is reached at idle before driving - this is to ensure oil gets to the right temp and viscosity and lubricates the turbo mechanicals eficiently. But should still drive off boost for some time before giving it welly to ensure oil temp is right up.

With regards to the original poster, it could be this "automatic choke", but unlikely due to the speeds you can reach without physically accellerating.

It sounds to me like the throttle is sticking. Get a mechanic to check it out ;)

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